A Heart-to-Heart on Drug-Eluting ePTFE for Cardio Applications

Debuting at this year's MD&M Minneapolis trade show, the MedTech Cardio Conference will address key issues and challenges in cardiovascular device design and development. As part of this thought-leadership forum, Lisa Jennings, a professor at the University of Tennessee Health Science Center and founder and CSO of Ariste Medical Inc. (Memphis, TN), will be pulling double duty as both a participant in a panel discussion and a session presenter. MPMN caught up with Jennings to discuss the future of cardiovascular device design, including her work with a novel drug-eluting ePTFE coating. For more information on the conference, visit www.medtechcardio.com.

MPMN: What are the most promising opportunities for advancing cardiovascular product development?

Jennings: Cardiovascular products have seen clinical success for decades now. Traditionally, advances in this field have been the result of design revisions or have centered on the development of novel implantation procedures, such as the minimally invasive deployment of shape-memory stents via a balloon catheter. But the more-recent and rapidly growing knowledge of cardiovascular biology and novel drug development and discovery offers new avenues for device and instrumentation improvements. We now have a far more advanced understanding of how blood and cardiovascular tissue interact with these products and the factors that lead to complications, for example. In addition, the ever-expanding and more-targeted drug selections that are becoming available allow for a more-defined mechanism of improvement for many conventional devices and open the door for the use of materials that were not traditionally viewed as viable options. Intervening upon specific physiological pathways that lead to product failure through the use of bioactive agents will allow us to transcend biologically installed hurdles that, until recently, were impossible to overcome.

MPMN: What are the most significant barriers to innovation in cardio device design and development?

Jennings: One of the most significant barriers to innovation is elucidating the most appropriate mechanism of action to achieve the desired outcome. In the setting of device-induced tissue damage with a metal coronary stent, for example, is it better to inhibit the damaged tissue with an antiproliferative therapy or to 'heal' the tissue with a proendothelial cell agent? We've seen that the antiproliferative therapy works to prevent restenosis but leaves a residual risk of late thrombosis.
Pertinent to the focus of the MedTech Cardio Conference, small-diameter stent grafts are saddled with increased incidence of thrombosis due to high shear rates in the narrow coronary vessels. In this case, an antithrombotic target may be an ideal approach to reduce incidence of failure. So, we are very focused on which pathway will deliver the goal for improved patient outcomes. These examples are just a few among many that illustrate how we are just beginning to understand the biology of vascular injury response and how to regulate it effectively. Advancing our understanding of recent discoveries in biology will significantly reduce barriers to innovation.

MPMN: What are some of the current limitations of drug-coating technologies?

Jennings: I see two main limitations when performing drug-coating technology overviews. First, many drug coatings employ polymer technologies that are foreign to the medical field. Both regulatory agencies and medical professionals are hesitant to embrace these technologies as acceptable for implantation within the body due to a lack of background biocompatibility and performance data. Second, it has recently become popular to chemically bond agents to the surfaces of products. This incorporation method may be very effective along the surface planes of a device, but no tissue is truly two dimensional. In order to maximize the effects of incorporating bioagents within a device, these agents need access within tissue beyond the minor portions in direct contact with the surface of a device. Also, it is important to control the exposure of these drugs to the surrounding tissue in order to achieve the desired biologic response.

MPMN: You will be presenting on an innovative drug-eluting ePTFE technology at the MedTech Cardio conference. What properties of ePTFE make it desirable for use in drug-eluting cardiovascular products?

Jennings: This is an interesting question because the properties of ePTFE actually make it quite unsuitable for drug delivery. In fact, its chemical inertness and physiochemical nature tend to repel most compounds, resulting in difficulty when it is coated with drugs or drug-eluting polymers. However, there is a great desire to elute drugs from ePTFE based on its superior blood biocompatibility compared with other related materials, such as Dacron, polyurethane, carbothane, etc. It is, and has been, a commonly used material in medical devices since the 1960s, and the potential to transform legacy devices into drug-delivery platforms is exciting.

MPMN: Please explain briefly your company's drug-eluting ePTFE technology and why you think it is unique.

Jennings: As stated, ePTFE is traditionally a very challenging coating substrate to work with due to its inherent inert chemical attributes and, even more so, because of its physiochemical ability to repel most compounds. Although these features may ease the burden of cleaning Teflon-coated cooking pans, they complicate efforts to adhere compounds to ePTFE in the medical device sector. Ariste's technology overcomes these challenges, however, and allows for localization of our drug-eluting coating onto the node--or island--microstructures of the ePTFE while preserving the material's beneficial open interstitial porosity.

MPMN: What benefit could Ariste's drug-eluting ePTFE technology ultimately have for patients and physicians?

Jennings: We have successfully incorporated and eluted a handful of bioactive agents from ePTFE surfaces to date. Within the cardiovascular arena, we are currently considering the incorporation of antimicrobial, antiproliferative, antiinflammatory, and antithrombotic agents individually as well as in combination. These various agents have the ability to increase the success rate of the traditional ePTFE devices that are currently on the market. Furthermore, an Ariste drug-eluting device would be used in the same, familiar manner as a traditional device. Reduced complications--such as infection, stenosis, and thrombotic events--as well as increased patency and faster recovery times will benefit both patients and physicians. Less-frequent operations will also reduce societal expenses and improve patient quality of life.